"It just kind of hits you in the gut when you see this thing strengthening and know that the forecast is calling for it to come in as such a strong storm," he told CNN on Monday after his third flight. "We don't like what we're seeing. I don't think you guys like much what you're seeing on the ground either."

Hurricane hunters have monitored the storm from above over the last few days as it churns toward the southern East Coast of the United States. Hurricane Florence neared Category 5 strength on Monday, forcing evacuations in coastal areas in North Carolina, South Carolina and Virginia.

NOAA Hurricane Hunter Pilot Cmdr. Justin Kibbey also recalled the distinctness of the storm's eye. It stretched 10 to 12 miles, he said.

"This storm has really got its act together and it's just a heck of a storm out there," Kibbey told CNN.

Kibbey described "moments of intensity, followed by some lulls" as he flew in and out of the storm.

The 2017 hurricane season kept hurricane hunters like Kibbey busy. Two storms, Harvey and Irma, killed more than 140 people in the southeast and caused hundreds of billions of dollars in damages. Puerto Rico's government raised Hurricane Maria's official death toll to 2,975 last month after maintaining for months that 64 people had died.

"It's on par with the storms we flew last year, like Maria and Irma," Kibbey said.

Flaherty, who is also a meteorologist, said the storm is "life-threatening."

"We want to make sure that we get the best data going to the National Hurricane Center ... and to emergency managers and to the media so we can get people out of the way," Flaherty said.

More than a million people in the southeast United States faced mandatory evacuation orders. Flaherty urged people to heed those warnings.

"Every time there's going to be those people who decide to stay," he said. "We read about their names and their stories, and we want to try to know why they didn't go."